Donald F. Eldridge graduated from Lehigh in 1949 with a BS in electrical engineering. He worked for Ampex, a visual information technology company, then co-founded Memorex, a leading manufacturer of audio and video recording media. Prior to his time at Ampex and Memorex, Eldridge was employed for seven years with Boeing Airplane Company, Seattle. In 1954, with the permission of Boeing, Eldridge formed and became president of Sonic Instrument Company which made rugged high-impedance cathode followers, power supplies, vibration transducers and an automatic 96-channel bridge-balancing device. In 1956 he abandoned his work with Sonic Instrument Company and Boeing in order to join the Corporate Research Division of Ampex Corporation. Here he spent much of his time researching and becoming an expert on magnetics, thus leading him to attain a technical leadership position of Manager of the Magnetics Department at Ampex.
Throughout his career Eldridge presented technical papers at WESCON, IRE National convention and the Conference on Magnetism and Magnetic Materials. He also held the position of National Chairman of the Professional Group on Magnetic Recording, whose elected membership is generally considered to represent the "Who's Who" of the magnetic tape recording industry.